1. Field of the Invention
The present invention relates to a pressure sensor.
2. Description of Related Art
An occupant restraint system is typically mounted to a vehicle, and protects an occupant when the vehicle collides with an object. For example, an air-bag device for protecting a head of the occupant by inflating an air-bag, or a pretensioner for tensioning a seatbelt is used as the occupant restraint system. The air-bag device or the pretensioner is controlled by an electrical control unit (ECU). The ECU determines collision of the vehicle based on a signal output from a sensor provided in the vehicle, and activates the occupant restraint system based on the determination.
Not only a safety for collision in a vehicle traveling direction (back- and forth direction of the vehicle) but also a safety for lateral collision in a vehicle width direction is required, recently. JP-A-2-249740 discloses a side air-bag device for protecting the occupant from the lateral collision. A pressure variation in a space is detected in order to inflate the side air-bag device. A pressure sensor detects a variation of an inner pressure inside of a door of the vehicle as the pressure variation in the space.
The pressure sensor for detecting the lateral collision includes a case and a circuit assembly. The case has an approximately hollow body, and an air passage is provided in the case in order to make inside of the case and outside of the case to communicate with each other. The circuit assembly is fixed in the case, and includes a sensor element for detecting a pressure. A rubber gasket is provided between the case and the sensor element, because a high water-resistance is required for the pressure sensor. Water can be restricted from seeping into the case except for a surface of the sensor element due to the rubber gasket disposed between the circuit assembly and the case. Thus, a circuit board of the circuit assembly can be kept dry.
However, when the rubber gasket is used in the pressure sensor, cost of the pressure sensor may be increased, because high dimensional accuracy is required for the circuit board, the sensor element and the case. Further, the rubber gasket is pressed between a detector of the circuit board and the case. That is, a stress for pressing the rubber gasket is applied to an electrical connection part between the circuit board and the sensor element. Therefore, reliability for the electrical connection part, the circuit board and the sensor element is difficult to be secured.